INTERFACIAL FREE RADICAL POLYMERIZATION MICROENCAPSULATION - KINETICSOF PARTICLE FORMATION/

Microcapsules containing pigment and polymer were prepared by dispersi ng a viscous mixture of pigment, core monomers, initiators and oil-sol uble shell monomer in an aqueous solution of surfactants, forming oil- in-water droplets. Subsequently, a water-soluble shell monomer was add ed to these droplets, encapsulating them via interfacial (IF) polycond ensation. These microcapsules were then heated for free radical (FR) p olymerization of the core monomers. Effects of primary variables, such as the shearing time during particle formation, surfactant concentrat ion, organic phase concentration, and mode of water-soluble shell mono mer addition, were studied. The results indicated that polyvinylalcoho l (PVOH), used as the surfactant/stabilizer, reacted with the oil-solu ble shell monomers. The depletion of PVOH, especially when PVOH concen tration was low, resulted in rapid growth of particle size and, eventu ally, suspension failure. The kinetic data revealed a particle formati on mechanism which consists of two processes. The first process is the formation of an equilibrium particle size by the equilibrium process of particle breakage due to the mechanical shearing force and coalesce nce due to collisions among particles and surface tension forces. The second process is the reaction between PVOH and oil-soluble shell mono mer which leads to the depletion of PVOH and consequently causes more coalescence of particles and a significant increase in the equilibrium particle size. The net effect of these two processes shows an optimum shearing time where the smallest particle size can be attained, and t his optimum time is a function of several primary variables. Methods t o prevent the reaction and therefore the depletion of PVOH are propose d.